94' 150 XR6 Hot/Very Warm @ Idle

**18ProCXR6** · 07-01-2016, 03:48 PM

I have a 1994 Merc 150 XR6. I know little to nothing about this motors past. Just picked it up last month and have been slowly doing some general maintenance items while I do some work on the boat. I've owned several other V6 mercs so I know my way around them. Deleted the oil injection. I've replaced the water pump, thermostats and poppet valve.
Motor comes up to operating temperature faster than I've ever seen (on the garden hose) and if I start it, and do not raise the idle, it will not pump water through the tattle tale. If I raise the idle just a tad, it will start pumping, but it almost has a surging effect to it. I haven't had a temp gun on the water yet and it's not steaming, but you definitely do not want to have your hand in it for very long. As soon as I raise the idle to say 1500 rpm, it cools right down. I've checked every external hose and fitting for a blockage and found nothing. I can touch each cylinder around the block and heads and no cylinder or side seems to be hotter than the other. I've taken the thermostat housings off and fired it up to make sure I didn't make any dumb mistakes replacing the water pump, and it only took a few seconds before water started pumping out the top of the heads at what seems like a normal rate for any V6merc. I am really starting to scratch my head on this one. Any ideas would greatly be appreciated before I start completely over.

**j_martin** · 07-01-2016, 05:03 PM

It sounds normal for running on cold water. All the water at the tattle tale has come through the thermostats, so it will definitely cook you. If there's steady flow out the prop, yer golden.

Is it possible you put the stats in backwards? Are they mercury stats, or some other maker?

**tlwjkw** · 07-02-2016, 09:07 AM

Originally Posted by 18ProCXR6

I've replaced the water pump,

base, stainless ride plate and housing or jus impeller?

**18ProCXR6** · 07-05-2016, 09:07 PM

Complete water pump kit. Originally being a saltwater guy, I never replace just impellers. Its always been my routine that once a year, the spark plugs, thermostats, complete water pump kit, gear oil gets changed. No questions asked.

****update**** out of frustration, I replaced every rubber hose on the power head. (never found a damaged hose). Combined with making some timing\idle adjustments, it pumps water at idle now. Used a thermometer to monitor the discharge water temp, never raises above 140. I guess I am just being paranoid, but neither of my previous EFI motors came up to operating temp this fast. Used to have a 98' 200 EFI & 04' 200 EFI Saltwater series. This is my first venture into the Carburetor world.

I dumped it in the lake and idled it around for about a hour, no water pumping or over heating issues. Still need to adjust static timing/idle its a little low, but I am currently chasing a inconsistent tach reading.

**rayhawk** · 07-07-2016, 12:34 PM

Check the bypass fitting on the poppet valve cover plate, I have the same motor and found it was clogged recently. I did a bunch of other work so I can't say for sure if it was causing an issue but it runs much cooler at idle now. To be honest I'm not even sure what that bypass is for but it might be worth a quick check.